Special effect lighting can be generally categorized according to the type of light used to achieve the effect. One type of light that is used to produce special effects is "white light", which is the spectrum of light that is visible to humans and seen, for example, in a rainbow. One type of white light special effect involves the placement of two overlapping disks between a white light source and a projection surface to achieve various effects. The disks have holes or windows that permit light to pass through. Upon rotation of the disks, the windows associated with one of the disks occasionally line up with windows associated with the other disk so that light from the white light source passes through the disks and onto the projection surface. By appropriately selecting the positions of the windows, various special effects can be achieved. For example, a random pattern of windows can be used to achieve a "snowfall" effect.
Separate from white light special effects are "blacklight" special effects that use ultraviolet light, which is outside the spectrum of light that is generally visible to humans, to produce the special effect. Because ultraviolet light or blacklight cannot be seen, these special effects also involve a projection surface that has been treated with a blacklight paint or similar substance that when irradiated with ultraviolet light, produces visible light. However, the visible light that is produced is relatively faint. The faint light produced in blacklight special effects provides the "eerie" glow that makes blacklight special effects especially appropriate in, for example, the haunted house rides in amusement and theme parks. However, due to the faintness of the light produced in a blacklight special effects, the effect can be easily ruined or washed out by white light. Consequently, the implementation of a blacklight special effect generally requires greater attention to the design of the environment in which the effect is to occur than does the typical white light special effect. One type of blacklight special effect involves the placement of a rotating disk between the blacklight source and the projection surface. The disk has one or more windows that permit the blacklight to pass through and onto the projection surface. Rotation of the disk creates a flickering or strobing effect, i.e. the ultraviolet light is permitted to pass by the windows to pass onto the projection surface and then prevented from passing onto the projection surface by opaque areas that are located between the windows on the disk.